Methods of recovering terbium oxide from a glass

ABSTRACT

A method for recovering Tb 4  O 7  from a glass containing terbium oxide is disclosed, the method including the steps of: 
     I. fusing the glass containing terbium oxide with NaOH to provide a solid fusion product; 
     Ii. slurrying the fusion product of Step I to disperse solid particles of Tb 4  O 7  and any Li 2  SiO 3  present and to dissolve any Al 2  O 3 , NaOH and Na 2  SiO 3  to thereby separate the same from the solid particles of Tb 4  O 7  ; 
     Iii. reacting the solid particles of Tb 4  O 7  of Step II with HNO 3  to provide Tb(NO 3 ) 3  ; 
     Iv. reacting the Tb(NO 3 )3with oxalic acid to form Tb 2  (C 2  O 4 ) 3  ; and 
     V. firing the Tb 2  (C 2  O 4 ) 3  to form CO 2  and solid Tb 4  O 7  to that is recovered from the glass.

INVENTION

The present invention is directed to recovering Tb₄ O₇ from a glass containing terbium oxide and, more particularly, is directed to recovering Tb₄ O₇ from a glass containing terbium oxide and contaminated with small amounts of platinum.

The present invention provides a convenient and economical method of obtaining Tb₄ O₇, which is costly and often difficult to obtain.

It is an object of the present invention to provide a method of recovering Tb₄ O₇ from a laser glass containing terbium oxide and small contaminating amounts of platinum.

It is an object of the present invention to provide a method of recovering Tb₄ O₇ from a laser glass containing terbium oxide, the method comprising the steps of:

I. fusing the glass containing terbium oxide with NaOH to provide a solid fusion product;

Ii. slurrying the fusion product of Step I to disperse solid particles of Tb₄ O₇ and to dissolve any Al₂ O₃, NaOH and Na₂ SiO₃ present in the fusion product to thereby separate from the other ingredients solid particles of Tb₄ O₇ + any Li₂ SiO₃ formed;

Iii. reacting the solid particles of Tb₄ O₇ separated from the slurry of Step II with HnO₃ to form Tb(NO₃)₃ ;

Iv. reacting Tb(NO₃)₃ with oxalic acid to form terbium oxalate; and

V. firing the terbium oxalate to form solid Tb₄ O₇ and CO₂, which CO₂ volatilizes off as a gas and is separated from the solid Tb₄ O₇.

These and other objects will be apparent from the specification that follows and the appended claims.

The present invention provides an economical and convenient method for recovering Tb₄ O₇ from a glass containing terbium oxide, including glass such as laser glass having contaminating amounts of platinum. The method comprises the steps of:

I. fusing the glass containing terbium oxide with NaOH to provide a solid fusion product;

Ii. separating the solid particles of Tb₄ O₇ from any Al₂ O₃, NaOH and Na₂ SiO₃ present by slurrying the fusion product of Step I to provide solid particles of Tb₄ O₇ and any Li₂ SiO₃ present;

Iii. reacting the solid particles of Tb₄ O₇ of Step II with HNO₃ to provide terbium nitrate;

Iv. reacting terbium nitrate with oxalic acid to form terbium oxalate as a reaction product thereof; and

V. firing the terbium oxalate to form CO₂, which is volatilized off as a gas and to form solid Tb₄ O₇ that is recovered. The fusing of Step I is suitably carried out at about 500° C.

The methods of this invention were developed in one preferred embodiment for the recovery of terbium oxide from a laser or Faraday rotator glass having contaminated amounts of platinum, the recovered terbium oxide then being advantageously available for subsequent reuse. The methods of this invention are convenient and advantageous.

In one preferred embodiment of the present invention, the laser glass or light rotating glass for use in a Faraday rotator device is a glass containing about 41% by weight of terbium oxide, the remainder of the composition containing silica, alumina and lithium oxide. A suitable light-rotating glass containing terbium oxide is one of the lithia-silica-terbia systems generally comprising, on a mole basis, about 61-80 mole percent SiO₂, 15-27.5 mole percent Li₂ O, 3-9 mole percent terbium oxide, and optionally, up to about 3 mole percent of R₂ O₃, such as La₂ O₃, Al₂ O₃ or B₂ O₃, and optionally, minor amounts of Na₂ O, K₂ O or CaO, namely, 0-10 Na₂ O, 0-5 K₂ O and 0-5 CaO. The sum of Li₂ O + Na₂ O + K₂ O + CaO should not generally be greater than about 32.5 mole percent.

A suitable glass for a Faraday rotation device is described in U.S. Pat. No. 3,484,152 to Robinson. One suitable terbium oxide-alumina silicate glass, as therein disclosed, is one containing in weight percent about 12% Al₂ O₃, 25% SiO₂, 4% MgO, 1% Pr₂ O₃ and 58% Tb₂ O₃.

In accordance with the specific embodiment of the present invention, the glass containing 61 mole percent SiO₂, 27.5 mole percent Li₂ O, 2.5 mole percent Al₂ O₃ and 9 mole percent Tb₄ O₇ is powdered and fused with NaOH to provide a solid fusion product. The resultant fusion is slurried in water to disperse solid particles of Tb₄ O₇ and Li₂ SiO₃, and to dissolve the alumina, NaOH and Na₂ SiO₃ to thereby separate the latter ingredients from the solid particles of terbium oxide. Thereafter, solid particles of terbium oxide are reacted with HNO₃ to provide Tb (NO₃)₃, the insoluble solid products of terbium oxide being reslurried in water and the pH adjusted to 2 with nitric acid. The resulting reaction product is terbium nitrate, which is a soluble salt, and another reaction product is a stable silica salt. Thereafter, the terbium nitrate is reacted with oxalic acid to form Tb₂ (C₂ O₄)₃. Thus the oxalic acid forms a complex, insoluble salt with terbium, which is filtered free of the silica. The terbium oxalate is fired in a 1,000° C. furnace to provide the recovered terbium oxide. The terbium oxide is reported as Tb₄ O₇, it generally being a mixture of Tb₂ O₃ and TbO₂.

The resultant recovered terbium oxide was used in a laser glass composition, as above described, to provide a laser glass which was suitable. The resultant laser glass of a lithia-silica-terbia system had a good balance of properties, including a high Verdet constant, good light transmission, good melt properties, high damage threshold, and good forming properties, including a relatively wide working temperature range at approximately log₄ viscosity, being relatively seed-free and easily homogenized.

In accordance with the present invention, it is costly and sometimes difficult to obtain terbium oxide. In the present process, a sometimes scarce material is obtained from glass, which is, as in the case with the light rotating glass, contaminated with platinum, rending it useless. In accordance with the present invention, the glass is fused with sodium hydroxide, which fusion breaks the composition into single components which can be separated from one another. These separations are made by controlling the pH in the subsequent isolation steps. 

What is claimed is:
 1. A method of recovering Tb₄ O₇ from a glass containing terbium oxide, the method comprising the steps of:I. fusing the glass containing SiO₂, Li₂ O, Al₂ O₃ and terbium oxide with NaOH to provide a solid fusion product; Ii. slurrying in water the fusion product of Step I to disperse solid particles of Tb₄ O₇ and Li₂ SiO₃ and dissolving the Al₂ O₃, NaOH and Na₂ SiO₃ to thereby separate said Al₂ O₃, NaOH and Na₂ SiO₃ from the solid particles of Tb₄ O₇ ; Iii. reacting the solid particles of Tb₄ O₇ separated from the slurry of step II with HNO₃ to provide Tb(NO₃)₃ ; Iv. reacting Tb(NO₃)₃ with oxalic acid to form Tb₂ (C₂ O₄)₃ ; and V. firing Tb₂ (C₂ O₄)₃ to form Tb₄ O₇ and CO₂ to thereby recover solid Tb₄ O₇.
 2. A method as defined in claim 1 in which the glass composition is a light rotating glass.
 3. A method as defined in claim 1 in which the glass has the following approximate composition:

    ______________________________________                                         Ingredients         Mole Percent                                               ______________________________________                                         SiO.sub.2           61 - 80                                                    Li.sub.2 O            15 - 27.5                                                Na.sub.2 O           0 - 10                                                    K.sub.2 O           0 - 5                                                      CaO                 0 - 5                                                      Al.sub.2 O.sub.3    0 - 3                                                      B.sub.2 O.sub.3     0 - 3                                                      La.sub.2 O.sub.3    0 - 3                                                      Terbium Oxide       3 - 9                                                      ______________________________________                                    

wherein the sum of Li₂ O + Na₂ O + K₂ O + CaO is no more than about 32.5 mole percent.
 4. A method as defined in claim 1 in which the reaction of Step III is at a pH of about
 2. 5. A method as defined in claim 1 in which the firing temperature of Step V is about 1,000° C.
 6. A method as defined in claim 1 in which the fusing of Step I is at about 500° C. 